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Class 12 Continuity And Differentiability · Long Answer3 Marksimplicit_differentiation

Class 12 Maths · Continuity And Differentiability · Long Answer #79

If x sin(a+y)+sin a cos(a+y)=0, prove y′=sin²(a+y)/sin a where sin a≠0 and sin(a+y)≠0.

✅ Step-by-Step Solution

Final Answer: sin²(a+y)/sin a
  1. Divide the relation by sin(a+y): x=−sin a cot(a+y).
  2. Differentiate with respect to y: dx/dy=sin a cosec²(a+y).
  3. This is nonzero under the stated assumptions, so invert it: dy/dx=1/[sin a cosec²(a+y)].
  4. Therefore y′=sin²(a+y)/sin a.

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] Divide the relation by sin(a+y): x=−sin a cot(a+y).
  • [1 mark] Differentiate with respect to y: dx/dy=sin a cosec²(a+y).
  • [1 mark] This is nonzero under the stated assumptions, so invert it: dy/dx=1/[sin a cosec²(a+y)].
  • [0.5 marks] Therefore y′=sin²(a+y)/sin a.

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